Implementing Custom Processor for Search API 1.x on Drupal 8

<?php

namespace Drupal\YOUR_MODULE\Plugin\search_api\processor;

use Drupal\search_api\Processor\FieldsProcessorPluginBase;

/**
 * Adds synonyms/alternate date formats for ISO 8601 dates.
 *
 * @SearchApiProcessor(
 *   id = "iso8601_date_synonymizer",
 *   label = @Translation("ISO 8601 date synonymizer"),
 *   description = @Translation("Adds alternative representations of ISO 8601-formatted dates at index time. For example, <em>1986-04-01</em> gets indexed as both <em>1986-04-01</em> and <em>April 1, 1986</em>. If using the 'ISO 8601 Date tokenizer', make sure this is invoked before it."),
 *   stages = {
 *     "pre_index_save" = -1,
 *     "preprocess_index" = -1,
 *   }
 * )
 */
class Iso8601DateSynonymizer extends FieldsProcessorPluginBase {

  /**
   * Matches ISO 8601 dates in the format YYYY-MM-DD, YYYY-MM, or YYYY.
   *
   * Each date component is captured in a named group.
   */
  const REGEX_ISO_8601_DATE_WITH_CAPTURE =
    '/^(?<year>[0-9]{4})(?>-(?<month>1[0-2]|0[1-9])(?>-(?<day>3[01]|0[1-9]|[12][0-9]))?)?$/';

  /**
   * {@inheritdoc}
   */
  protected function testType($type) {
    // Only apply to "text" types since we return the synonyms as distinct,
    // space-separated "words" (e.g. "1986-Apr-01 Apr-1986"), so in order for
    // searches to match, the index needs to treat this as full-text. Otherwise,
    // the user would have to search for *exactly* "1986-Apr-01 Apr-1986",
    // which isn't helpful.
    return $this->getDataTypeHelper()->isTextType($type);
  }

  /**
   * {@inheritdoc}
   */
  protected function process(&$value) {
    // In the absence of the tokenizer processor, this ensures split words.
    $words =
      preg_split('/\s/', strip_tags($value), -1, PREG_SPLIT_NO_EMPTY);

    $new_words = [];

    foreach ($words as $word) {
      $date_synonyms = $this->getDateSynonyms($word);

      // Keep original, unmodified value.
      $new_words[] = $word;

      if (!empty($date_synonyms)) {
        $new_words[] = implode(' ', $date_synonyms);
      }
    }

    $value = implode(' ', $new_words);
  }

  /**
   * Gets all the alternative ways to format the given date string.
   *
   * @param string $value
   *   A date string for which synonyms/alternate formats are desired.
   *
   * @return string[]
   *   An array containing all the alternate ways to format the given date. For
   *   example:
   *   @code
   *   [
   *     '04/01/1986',
   *     '04/01/86',
   *     '01/04/1986',
   *     '01/04/86',
   *     '01-Apr-1986',
   *     '01 Apr 1986',
   *     'April 01, 1986',
   *     'Apr-1986',
   *     'Apr 1986',
   *     'April 1986',
   *   ]
   * @endcode
   */
  protected function getDateSynonyms(string $value): array {
    $synonyms = [];

    if (preg_match(self::REGEX_ISO_8601_DATE_WITH_CAPTURE, $value, $matches)) {
      $month_number = $matches['month'] ?? NULL;
      $day_number   = $matches['day'] ?? NULL;

      if ($day_number !== NULL) {
        $date = \DateTime::createFromFormat('!Y-m-d', $value);

        // US - "04/01/1986".
        $synonyms[] = $date->format('m/d/Y');

        // US - "04/01/86".
        $synonyms[] = $date->format('m/d/y');

        // EU - "01/04/1986".
        $synonyms[] = $date->format('d/m/Y');

        // EU - "01/04/86".
        $synonyms[] = $date->format('d/m/y');

        // "01-Apr-1986".
        $synonyms[] = $date->format('d-M-Y');

        // "01 Apr 1986".
        $synonyms[] = $date->format('d M Y');

        // "April 01, 1986".
        $synonyms[] = $date->format('F d, Y');
      }
      elseif ($month_number !== NULL) {
        $date = \DateTime::createFromFormat('!Y-m', $value);
      }

      if (isset($date)) {
        // "Apr-1986".
        $synonyms[] = $date->format('M-Y');

        // "Apr 1986".
        $synonyms[] = $date->format('M Y');

        // "April 1986".
        $synonyms[] = $date->format('F Y');
      }
    }

    return $synonyms;
  }

}

<?php

namespace Drupal\YOUR_MODULE\Plugin\search_api\processor;

use Drupal\search_api\Processor\FieldsProcessorPluginBase;

/**
 * Tokenizes ISO 8601 dates into YYYY-MM-DD, YYYY-MM, and YYYY formats.
 *
 * @SearchApiProcessor(
 *   id = "iso8601_date_tokenizer",
 *   label = @Translation("ISO 8601 date tokenizer"),
 *   description = @Translation("Tokenizes ISO 8601-formatted dates at index time. For example, <em>1986-04-01</em> gets indexed as <em>1986-04-01</em>, <em>1986-04</em>, and <em>1986</em>."),
 *   stages = {
 *     "pre_index_save" = 0,
 *     "preprocess_index" = 0,
 *   }
 * )
 */
class Iso8601DateTokenizer extends FieldsProcessorPluginBase {

  /**
   * Matches ISO 8601 dates in the format YYYY-MM-DD, YYYY-MM, or YYYY.
   */
  const REGEX_ISO_8601_DATE =
    '/^([0-9]{4})(?>-(1[0-2]|0[1-9])(?>-(3[01]|0[1-9]|[12][0-9]))?)?$/';

  /**
   * {@inheritdoc}
   */
  protected function testType($type) {
    // Only apply to "text" types since we return the permutations as distinct,
    // space-separated "words" (e.g. "1986-04-01 1986-04 1986"), so in order for
    // searches to match, the index needs to treat this as full-text. Otherwise,
    // the user would have to search for *exactly* "1986-04-01 1986-04 1986",
    // which isn't helpful.
    return $this->getDataTypeHelper()->isTextType($type);
  }

  /**
   * {@inheritdoc}
   */
  protected function process(&$value) {
    // In the absence of the tokenizer processor, this ensures split words.
    $words =
      preg_split('/\s/', strip_tags($value), -1, PREG_SPLIT_NO_EMPTY);

    $new_words = [];

    foreach ($words as $word) {
      $date_permutations = $this->getDatePermutations($word);

      if (empty($date_permutations)) {
        // Pass through unmodified.
        $new_words[] = $word;
      }
      else {
        $new_words[] = implode(' ', $date_permutations);
      }
    }

    $value = implode(' ', $new_words);
  }

  /**
   * Gets all the substrings that should match on the given date string.
   *
   * @param string $value
   *   A date string for which token permutations are desired.
   *
   * @return string[]
   *   All token permutations for the given date. For example:
   *   @code
   *   [
   *    '1986-04-01',
   *    '1986-04',
   *    '1986',
   *   ]
   *   @endcode
   */
  protected function getDatePermutations(string $value): array {
    $permutations = [];

    if (preg_match(self::REGEX_ISO_8601_DATE, $value, $matches)) {
      $date_parts       = array_slice($matches, 1);
      $total_part_count = count($date_parts);

      for ($perm_index = 0; $perm_index < $total_part_count; ++$perm_index) {
        $permutations_parts =
          array_slice($date_parts, 0, $total_part_count - $perm_index);

        $permutations[] = implode('-', $permutations_parts);
      }
    }

    return $permutations;
  }

}